The present invention relates to an improved process for manufacturing an alternator pole piece. In an automobile, an alternator is commonly employed and driven via a belt coupled between the alternator and the automobile engine. Rotation of the alternator rotor results in the production of electrical power which is used, mainly, to recharge the storage battery carried by the automobile so that the automobile engine may be conveniently started as desired. In alternators as presently used in vehicles, the rotor rotates at speeds of as such as 15,000 to 22,000 revolutions per minute. In the automobile industry, at present, there is keen competition between various alternator manufacturers to provide the best alternator at the lowest price. However, the definition of the term "best" as it pertains to alternators is not always easy to comprehend.
The optimal alternator combines light weight with compact size, while providing high power output and low noise. At the heart of any alternator are the pole pieces, two in number, which are mounted in facing relationship with respect to one another on the rotor shaft and enclose, therebetween, the coil. The design of a pole piece is crucial to the enhancement of power output of an alternator and, at the same time, the pole piece is one of the greatest sources of noise generated by an alternator.
Unfortunately, steps which are taken to reduce the noise output caused by the structure of a pole piece often adversely affect the power output thereof. Additionally, the location of the center of gravity of the pole piece finger greatly affects the specific design of the gap between the rotor and stator. In this regard, with the center of gravity of the pole piece optimized, and the pole piece manufactured in an appropriate manner, the fingers of the pole piece are less likely to bend outwardly during high speed rotations of the rotor. Thus, optimal location of the center of gravity can facilitate narrowing of the gap between the rotor and stator and thereby enhancement of the power output of the alternator. However, if it is not possible to optimize the location of the center of gravity of the fingers of the pole piece, the above-described gap must be increased to account for the possibility that the fingers of the pole piece will flex outwardly during high speed rotations and, thereby, touch and damage the stator and therefore the alternator itself. In this regard, where a pole piece is made in a stamping operation with the fingers thereof subsequently bent out of the plane of the stamping, the direction of the grains of some of the fingers are at a sharp angle as compared to the base of the pole piece corresponding to the angle between the fingers and the base. Under such circumstances, the ability of the fingers to resist bending during high speed rotation is reduced. Thus, when a pole piece is made in a stamping process, the gap between the rotor and the stator must be increased to account for the probability that the fingers of the pole piece will flex outwardly during high speed rotations thereof.
As such, as should now be understood from the above discussion, the design of a pole piece for the rotor of an alternator necessarily involves compromise.
At the present level of the state-of-the-art, alternators provide sufficient power output for their size and weight that automobile manufacturers have now begun to concentrate on steps to be taken to reduce noise. The shapes and configurations of the fingers of the pole pieces are altered to enhance air flow therethrough without causing turbulence which creates noise. As such, a great need has developed for a manufacturing process which will optimize the power output of an alternator where the pole piece fingers have been designed more to enhance noise reduction than to enhance power output and therefore find the best compromise between both of these parameters. It is mainly with this problem in mind that the inventive process was developed.
In a further aspect, it is important to maintain the electrical coils of the rotor and stator of an alternator at as low a temperature as is possible. Thus, it has been known, in the past, to provide the rotor shaft with at least one ventilation fan mounted thereon exterior to the rotor housing. The ventilation fan communicates with the interior of the rotor housing via a series of slots formed therein. Such a design which is particularly shown in FIG. 1, herein, is inefficient due to the separation between the ventilation fan and the rotor. Furthermore, the use of a plurality of slots in the rotor housing causes increases in noise generation which are unacceptable to the automobile industry. Since the resistivity of copper increases with increases in temperature, efficient ventilation of an alternator will keep copper resistivity relatively low. Since copper resistivity is inversely proportional to current intensity, as the temperature increases, the current intensity in the coil of the alternator will necessarily decrease. Since magnetic flux is proportional to current intensity, the power output of an alternator is directly related to its temperature. Thus, a need has developed for an efficient system for cooling an alternator, which system does not appreciably increase noise generation thereof.